Method and material for metallizing ceramics



, 2,902,756 METHOD MATERIAL FOR METALLIZING;

- CERAMICS Daniel .i. Cavanaugh, Kearny, N.J., assignor to Radio Corporation of America, a corporation of Delaware .NoDrawing. Application October is, 1955 SerlalNo. 541,288

g -15 Claims. (Cl. 29-4731 'Ihis'inve ntion"relates to improved methods and mamenus for metallizingceramic bodies. More particularly,

States Patent 2,902,756 fiatentecl Sept. 8, a 1959 brushing the paste with a paint-like consistency onto the ceramic. surface.

The ceramic body which has thus been coated is then placed into a molybdenum boat, care being taken to pre- 5 vent' contact between the metal powder coating and-the surface .ofthe boat. Alternatively, instead of a molybi -denum boat, porous alumina plates may be employed.

one aspect of'the invention relates to an improved com- *pos'itionof'matter including tungsten and iron for metallizing' ceramic bodies.

{In general, thebonding of metallic coatings to ceramic bodiesisre'lativelydiflicult. One of the most successful -metallizfing materials for most ceramic bodies has been a verylittle bonding, if any, to beryllia cera- A further object of the invention is to provide an improved' method for metallizing beryllia or other ceramic bodies. i

:Briefly,lthese objects and other advantages of the invention are attained by the discovery that the addition of silicon dioxide and titanium dioxide to the tungsten-iron mixes previously' usedfor ceramic metallizing results in a strong adherent bond between the ceramic body and the metallic surface formed.

il' According to. a preferred example, beryllia ceramic +bodiesaremetallized .according to the invention by. first i-mixin'g; tungsten, iron, Si0 and TiO powders in the following proportions. To a tungsten-iron mixture of nine parts by weight tungsten and one part by weight iron;

about,.l8% by weight SiO and-3% ,by weight Ti0 is added! The particle size'ofthe tungsten and iron is preferably between 1 and 4 microns in order to assure intimate contact with the ceramic surface. Thus, the mixture comprises the previously used tungsten-iron mixture and about 21% SiO TiO of the weight of the tungsten and iron mixture, with the ratio of SiO;, to TiO being six to one. The powders are mixed thoroughly in the dry state and then are mixed into a paste by adding an ethyl acetate and nitrocellulose binder until a paint-like consistency is obtained. The binder may be any of those commonly used and known in the art, such as ethyl cellulose or methacrylate resins, which decompose upon heating leaving little or no residue. An excess amount of binder may be used to cause slow drying and to promote adherence to the beryllia surface. An illustrative example is 10 grams iron-tungsten, 2.1 grams Slo TiO in 3-4 cc. of a binder comprising about 1 gram of nitrocellulose per 43 cc. of ethyl acetate.

The paste containing the metallizing mixture is applied to the beryllia ceramic surface preferably with a camels hair brush. Other methods of applying the paste are possible such as by spraying or by dipping the body into the paste. -When applying the paste by brush, the paste should havea consistency comparable to that of paint. A smopth coating about .002 inch thick can be obtained by The molybdenum boat containing the coated ceramic is thenplaced in a furnace and fired in hydrogen at a temperature of about 1600 C. for about 5 to 10 minutes.

"Firing may be accomplished in any suitable reducing atmosphere although the best metal-to-ceramicbond appears to be obtained when the firing is in hydrogen. Another good reducing atmosphere which may be used is forming gas consisting of 5-10% hydrogen with the balance nitrogen. The firing temperature is not critical and depends upon the characteristics of the berylliaitself; Actually, temperatures between 150 and 16 5 0 have been found suitable. 20 1'.

'a strong adherent bond has been effected between the beryllia ceramic body and the metallizing tungsten-iron Upon the conclusion of the firing, it will be found that mixture. The metallized area can then be nickel or copper plated, if desired, so that the body may be brazed to another metallic body, with hard or soft solder. In general, the iron-tungsten metallized area is not easily wet for brazingpurposes, hence the desirability of plating the area with nickel or copper. After the metallized ceramic body is plated with nickelor copper it is placed in contact with the metal bodyor part to which it is to be brazed. The metallized-plated area is between the two bodies, Additional brazing materials and fluxes may be employed to enhance the brazing process. It has been found that hard or soft solders may be used for this purpose depending upon the ultimate use to which the joined bodies may be put; it intended for use in apparatus subject' to high operating temperatures, it is preferred to use fthe' hard solders because of their higher melting points.

.s'oftf solders it-is meant .to include solders containing relatively low melting point materials such as bismuth, lead, cadmium, or tin, for example. Hard solders .in-

,clude .materials having relatively higher melting points vfsrl 'ehf as silver or copper or alloys thereof; .These brazing 'materials are'well known and are commercially obtainable under various trade names. Typical suitable'pexamples are Sil-Fosl and.. BT Solder, manufactured and sold by Handy and Harman Co. of Bridgeport, Connecticut. Sil-Fos comprises copper, 15% silver, and 5% phosphorus; BT Solder is a eutectic solder comprising 28% copper and 72% silver. After the two bodies are in contact with the brazing material between the metal body and the plated-metallized portion of the ceramic body, the assembly is fired to make the braze.

The quantity of the SiO --TiO powder added to the standard tungsten-iron mixture may be varied considerably. The percentage by weight of the SiO -TiO in the example given was 21%; it has been found that the percentage by weight of the SiO -TiO may be varied from 18 to 28% of the weight of the tungsten and iron and still produce excellent bonding qualities. However, the best results are obtained by maintaining the SiO TiO ratio at about six to one. Thus, in the example given the 21% SiO TiO- comprises about 18% SiO and 3% TiO gAlthough a metallizing mixture of 9 parts by weight of tungsten to 1 part by weight of iron is preferred, the invention may be used with any other proportions of these elements. Beryllia bodies can be metallized according to the invention with iron or tungsten alone. However, the :strongest bond between the metal and ceramic is formed by the mixture of tungsten and iron in the preferred proportion given. In any case the percentage by weight of SiO TiO added is the same.

The invention is of particular advantage wherever it is desired to metallize beryllia ceramic bodies. Oneimportant application of the invention is theme tallizing of beryllia ceramic insulators so that they'can be brazed to a metallic cap in the manufacture of electron tubes where high thermal conductivity is required through the ceramic. Beryllia' is a particularly desirable ceramicto use where In many applications, however, it

the device in which used.- The invention thus is of great :advantage for permitting joinder of such beryllia bodies to metallic bodies. 7

What is claimed is: a

l. The method of metallizing the surface of a. ceramic body comprising the steps of: coating said surface with I a mixture of at least one element selected from the group consisting of iron and tungsten with Si and TiO said -SiO and TiO beingfrom 18 to 28% by weight of-s'aid coated body is fired in a reducing atmosphere of hydrogen.

4. The method according to claim 1 whereinsaid mixture comprises a tungsten-to-iron ratio of about9 to 1 and an Si0 TiO mixture weighing from 18 to 28% of.

the weight of the tungsten and the iron.

5. The method according to claim 4 wherein said coated body is fired in a reducing atmosphere of-hydrogen.

6. The method of metallizing the surface of a beryllia body comp-rising the steps of: coating said surface with a mixture of nine parts by weight of powdered tungsten from 18 to 28% of the tungsten-iron weighta mixture of SiO and TiO the ratio of said SiO toTiO being about six to-one, and firing said body having said coated surface in hydrogen at a temperature between 1550 and 7. The method according to claim 6 wherein said percentage of said SiO TiO mixture is 21% by weight of said tungsten-iron weight.

8. The method according. to claim 6 wherein said i firing temperature is about 1600" C. 7 50 ,to one part by weight of powdered iron and containing o 9. The method according to claim 6 including thestep of plating said metallized surface with a metal suitable for brazing.

10. The method according to claim 9 wherein said plated metal is selected from the group consisting of cop per and nickel.

11. The method according to claim 6 wherein said mix- .ture is suspended-in a heat-decomposable organic vehicle.

12. The method according to claim 11 wherein said vehicle containing said mixture is applied to saidgsurface to a thickness of about .002 inch.

13. The method of bonding a body of beryllia to a metallic body comprising thesteps: coating the-surface of 7 said beryllia body with a paste comprising a heat-do composable organic binder in whichhasjbeen suspended a mixture of nine parts by weight of powdered tungsten to one part by weight of powdered iron andcontaining a mixture of 18% SiO and 3% TiQ relativeto the weight of said powdered tungsten and powdered itemfiring; said body having said coated surface in hydrogenata temperature of1600 C. for about 5 to 10 minutes toform a metallized tungsten-iron area bonded to said surface of said body; plating said metallized area with a metal selected from the group consisting of copper and nickel; contacting said beryllia body to said metallic body with said plated metallized surface therebetween; and heating I said bodies to brazing temperature of said plated metal.

14. A metallizing composition for ceramic bodies consisting essentially of nine parts by weight of powdered tungsten to one part by weight of powdered iron and containing from about 18 to 28% of said tungsten and iron weight of a mixture of SlO' -aI1d-TlO the ratio of said Si0 to TiO being about six to one. I p 15. A metallizing composition for ceramic bodiescon- .sisting essentially of nine parts b weight of powdered tungsten to one part by weight of powdered iron and-about 18% by weight SiO and 3% by weight TiO relative;to the weight of said powderedtungsten and said powdered ll'OIl. e 

1. THE METHOD OF METALLIZING THE SURFACE OF A CERAMIC BODY COMPRISING THE STEPS OF: COATING SAID SURFACE WITH A MIXTURE OF AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF IRON AND TUNGSTEIN WITH SIO2 AND TIO2, SAID SIO2 AND TIO2 BEING FROM 18 TO 28% BY WEIGHT OF SAID IRON AND TUNGSTEN THE RATIO OF SAID SIO2 TO SAID TIO2 BEING ABOUT SIX TO ONE, AND FIRING SAID BODY HAVING SIAD COATED SURFACE AT A TEMPERATURE BETWEEN 1550* AND 1650*C.
 13. THE METHOD OF BONDING A BODY OF BERYLLIA TO A METALLIC BODY COMPRISING THE STEPS: COATING THE SURFACE OF SAID BERYLLIA BODY WITH A PASTE COMPRISING A HEAT-DECOMPOSABLE ORGANIC BINDER IN WHICH HAS BEEN SUSPENDED A MIXTURE OF NINE PARTS BY WEIGHT OF POWDERED TUNGSTEN TO ONE PART BY WEIGHT OF POWDERED IRON AND CONTAINING A MIXTURE OF 18% SIO2 AND 3% TIO2 RELATIVE TO THE WEIGHT OF SAID POWDERED TUNGSTEN AND POWDERED IRON; FIRING SAID BODY HAVING SAID COATED SURFACE IN HYDROGEN AT A TEMPERATURE OF 1600*C. FOR ABOUT 5 TO 10 MINUTES TO FORM A METALLIZED TUNGSTEN-IRON AREA BONDED TO SAID SURFACE OF SAID BODY; PLATING SAID METALLIC AREA WITH A METAL SELECTED FROM THE GROUP CONSISTING OF COPPER AND NICKEL; CONTACTING SAID BERYLIA BODY TO SAID MTALLIC BODY WITH SAID PLATED METALLIZED SURFACE THEREBETWEEN; AND HEATING SAID BODIES TO BRAZING TEMPERATURE OF SAID PLATED METAL.
 14. A METALLIZING COMPOSITION FOR CERAMIC BODIES CONSISTING ESSENTIALLY OF NINE PARTS BY WEIGHT OF POWDERED TUNGSTEN TO ONE PART BY WEIGHT OF POWDERED IRON AND CONTAINING FROM ABOUT 18 TO 28% OF SAID TUNGSTEN AND IRON WEIGHT OF A MIXTURE OF SIO2 AND TIO2 THE RATIO OF SAID SIO2 TO TIO2 BEING ABOUT SIX TO ONE. 